Method and Device for Calculating Combustion in Waste Incinerator Bed

Abstract

Disclosed is a method for calculating combustion in the bed of a waste incinerator. The method is based on a model of combustion in a waste incinerator bed and comprises a water evaporation model, a volatile matter analysis model, a volatile matter combustion model, and a fixed carbon combustion model. The volatile matter of the volatile matter combustion model comprises CO, H.sub.2, CH.sub.4, NH.sub.3, and H.sub.2S. The volatile matter combustion model comprises a combustion reaction equation for said volatile matter and O.sub.2, and respective equations for CO and CH.sub.4 reacting with water vapor. Equations governing the model of combustion in the bed of a waste incinerator comprise a continuity equation, an energy equation, a momentum equation, and a component equation. Boundary conditions of said governing equations comprise: equations of heat transfer and mass transfer from an upper boundary layer of the bed to the exterior; and equations of heat transfer and mass transfer from lower boundary layer of the bed to the exterior.

Claims

1. A method for calculating combustion in a bed of a waste incinerator, wherein the method is based on a model of combustion in the bed of the waste incinerator, the method comprises: receiving initial condition data; inputting the initial condition data into a governing equation of the model of combustion in the bed of the waste incinerator; calculating the governing equation to obtain a calculation result; displaying the calculation result; wherein the model of combustion in the bed of the waste incinerator comprises a moisture evaporation model, a volatile matter analysis model, a volatile matter combustion model, and a fixed carbon combustion model; wherein volatile matters in the volatile matter combustion model comprise CO, H.sub.2, CH.sub.4, NH.sub.3 and H.sub.2S, the volatile matter combustion model comprises a combustion reaction equation for said volatile matter and O.sub.2, and respective equations for CO and CH.sub.4 of the volatile matter reacting with water vapor; the governing equation for the model of combustion in the bed of the waste incinerator comprise a continuity equation, an energy equation, a momentum equation, and a component equation; a boundary condition of said governing equation comprise: a equation of heat and mass transfer from an upper boundary layer of the bed to the exterior; and a equations of heat and mass transfer from a lower boundary layer of the bed to the exterior, and wherein the mass transfer equation of the upper boundary layer of the bed to the exterior is: ${D_{g}A\frac{\partial Y_g}{\partial x}.Math.}_s={\mathrm{Ah}}_s\left(Y_{\infty }-Y_{g.s}\right)$ wherein A is an area of a bed interface, with a unit of m.sup.2; D.sub.g is a diffusion coefficient of a gas, with a unit of m.sup.2/s; h.sub.s is gas-solid two-phase mass transfer coefficient with a unit of m/s; Y.sub.∞ is a mass fraction of a gas component in the hearth; and Y.sub.g,s is a mass fraction of a gas component in the upper boundary layer; a heat transfer equation of the upper boundary layer of the bed to the exterior is: ${k_{\mathrm{eff}}A\frac{\partial T}{\partial x}.Math.}_s={\mathrm{Ah}}_T\left(T_{\infty }-T_{s1}\right)+A\mathrm{.Math.\sigma }\left(T_{\mathrm{rad}}^4-T_{s1}^4\right)$ wherein k.sub.eff is an effective thermal conductivity of the bed, with a unit of W/(m.Math.s), h.sub.T is a heat transfer coefficient, with a unit of W/(m.sup.2.Math.K); T.sub.∞ is temperature in the hearth, with a unit of K; T.sub.rad is radiation temperature with a unit of K; T.sub.s1 is temperature of the upper boundary layer, with a unit of K, ε is a radiation coefficient, ε is 0.8; σ is the Boltzmann's constant.

2. The method according to claim 1, wherein the initial condition data comprises: element analysis data, industrial analysis data, a low heating value (LHV) and raw material size data of a target waste; the calculation result comprises: a temperature distribution, a flow field distribution and a concentration distribution of gas components of the target waste in the bed during an incineration process, wherein the concentration distribution of gas components comprises concentration distributions of nitride and/or sulfide.

3. The method according to claim 1, wherein the continuity equation comprises a continuity equation of gas phase part and a continuity equation of solid phase part, the continuity equation of gas phase part is: $\frac{\partial \left({\mathrm{\varphi \rho }}_g\right)}{\partial t}+\mathrm{div}\left({\mathrm{\varphi \rho }}_{g}u\right)=S_g$ the continuity equation of solid phase part is: $\frac{\partial {\rho }_s}{\partial t}=-S_g$ wherein ϕ is a void fraction with a unit of %; ρ.sub.g is a density of a gas, with a unit of kg/m.sup.3; t is time in s; u is a flow rate of the gas, with a unit of m/s; ρ.sub.s is a density of a solid, with a unit of kg/m.sup.3; S.sub.g is a source phase of the continuity equation of gas phase.

4. The method according to claim 1, wherein the energy equation is: $\frac{\partial \left({\mathrm{\varphi \rho }}_g{C}_{\mathrm{pg}}T+\left(1-\varphi \right){\rho }_s{C}_{\mathrm{ps}}T\right)}{\partial t}+\mathrm{div}\left({\mathrm{\varphi \rho }}_g{\mathrm{uC}}_{\mathrm{pg}}T\right)=\mathrm{div}\left(k_{\mathrm{eff}}\nabla T\right)+S_T$ wherein T is reaction temperature, with a unit of K; C.sub.pg is a specific heat capacity of a gas, with a unit of J/kg; C.sub.ps is a specific heat capacity of a solid, with a unit of J/kg; k.sub.eff is an effective thermal conductivity of the bed, with a unit of W/(m.Math.s); S.sub.T is a source phase of the energy equation.

5. The method according to claim 4, wherein a calculation formula for the effective thermal conductivity k.sub.eff is: $k_{\mathrm{eff}}=k_{\mathrm{eff},0}+0.5{\mathrm{Pr}\mathrm{Re}k}_g$ $k_{\mathrm{eff},0}=\varphi \left(k_g+h_{\mathrm{rv}}\Delta l\right)+\frac{\left(1-\varphi \right)\Delta l}{1/\left(k_g/l_v+h_{\mathrm{rs}}\right)+l_s/k_s}$ wherein k.sub.eff,0 is an effective thermal conductivity in an absence of fluid, with a unit of W/(m.Math.s); Pr is Planck constant; Re is Reynolds number with a particle size of a solid particle as a characteristic length; k.sub.g is a thermal conductivity of a gas, with a unit of W/(m.Math.K); h.sub.rv is an effective radiant heat transfer coefficient in a void, with a unit of W/(m.sup.2.Math.K); h.sub.rs is an effective radiant heat transfer coefficient of a solid contact surface, with a unit of W/(m.sup.2.Math.K); Δl is a characteristic length between two solid particles, with a unit of mm; l.sub.s is an equivalent thickness of a fluid calculation layer, with a unit of mm; k.sub.s is a thermal conductivity of a solid, with a unit of W/(m.Math.K); and l.sub.v is a thickness of a gas-solid contact layer, with a unit of mm.

6. The method according to claim 1, wherein the momentum equation is: $\frac{\partial \left({\mathrm{\varphi \rho }}_{g}u\right)}{\partial t}+\mathrm{div}\left({\mathrm{\varphi \rho }}_g\mathrm{uu}\right)=-\nabla P-\frac{\mu u}{K}-{\mathrm{\beta \rho }}_g{u}^2$ wherein P is a pressure of a gas, with a unit of Pa; K is a permeability of a porous medium, with a unit of %; β is a traction coefficient.

7. The method according to claim 1, wherein the component equation comprises a component equation of gas phase part and a component equation of solid phase part, the component equation of gas phase part is: $\frac{\partial \left({\mathrm{\varphi \rho }}_g{Y}_{\mathrm{ig}}\right)}{\partial t}+\mathrm{div}\left({\mathrm{\varphi \rho }}_g{\mathrm{uY}}_{\mathrm{ig}}\right)=\mathrm{div}\left(D_{\mathrm{ig}}\nabla Y_{\mathrm{ig}}\right)+S_{Y_{\mathrm{ig}}}$ wherein Y.sub.ig is a mass fraction of an i-th gas component in a mixed gas; D.sub.ig is a diffusion coefficient of an i-th gas component in the mixed gas, with a unit of m.sup.2/s; and S.sub.Y.sub.ig is source phase of a corresponding component; the component equation of solid phase part is: $\frac{\partial {\rho }_{\mathrm{is}}}{\partial t}=r_{\mathrm{is}}$ wherein ρ.sub.is is a density of an i-th component in a solid particle, with a unit of kg/m.sup.3; r.sub.is is a reaction rate of an i-th component in the solid particle, with a unit of kg/(m.sup.3.Math.s).

8. (canceled)

9. The method according to claim 1, wherein mass transfer equation of the lower boundary layer of the bed to the exterior is: ${D_{g}A\frac{\partial Y_g}{\partial x}.Math.}_s={\mathrm{Ah}}_s\left(Y_{\mathrm{in}}-Y_{g,s}\right)$ wherein D.sub.g is a diffusion coefficient of a gas, with a unit of m.sup.2/s; h.sub.s is a mass transfer coefficient with a unit of m/s; Y.sub.in is a mass fraction of a component gas in the exterior; Y.sub.g,s is a mass fraction of a component gas in the lower boundary layer; heat transfer equation of the lower boundary layer of the bed to the exterior is: ${k_{\mathrm{eff}}A\frac{\partial t}{\partial x}.Math.}_s={\mathrm{Ah}}_T\left(T_{\mathrm{in}}-T_{s2}\right)+A\mathrm{.Math.\sigma }\left(T_{\mathrm{in}}^4-T_{s2}^4\right)$ wherein k.sub.eff is an effective thermal conductivity of the bed, with a unit of W/(m.Math.s); h.sub.T is a heat transfer coefficient with a unit of W/(m.sup.2.Math.K); T.sub.in is temperature of the exterior with a unit of K; T.sub.s2 is temperature of the lower boundary layer with a unit of K.

10. A device for calculating combustion in a bed of a waste incinerator, wherein the device is based on the method according to claim 1, the device comprises: a data receiving module for receiving initial condition data; a data inputting module for inputting the initial condition data into a governing equation of a model of combustion in the bed of the waste incinerator; a calculation processing module for calculating the governing equation, to obtain a calculation result; a result display module for displaying the calculation result.

11. An apparatus for calculating combustion in a bed of a waste incinerator, wherein the apparatus is based on the method according to claim 1, comprises: a memory for storing a computer program; a processor for running the computer program stored in the memory to execute the method according to claim 1.

12. A non-transitory computer-readable storage medium on which computer program instructions are stored, wherein the computer program instructions, when executed by the processor, implement the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 is a schematic diagram of an incineration process of solid particles in a waste according to the present invention.

[0044] FIG. 2 is a schematic diagram of a modeling process for a combustion model of a bed of a waste incinerator according to the present invention.

[0045] FIG. 3 is a calculation area for a combustion in a bed of a waste incinerator according to the present invention.

[0046] FIG. 4 is a graph of percentages of residual mass of solid wastes in a bed.

[0047] FIG. 5 is a curve graph of temperature at different height positions of a bed.

[0048] FIG. 6 is a curve graph of temperature variations and velocity variations at the top of a calculation area.

[0049] FIG. 7 is a comparison chart of calculation results versus experimental results for oxygen concentration at 430 mm.

[0050] FIG. 8 is a comparison chart of calculation results versus experimental results for carbon dioxide concentration at 430 mm.

[0051] FIG. 9 is a comparison chart of calculation results versus experimental results for carbon monoxide concentration at 430 mm.

DESCRIPTION OF REFERENCE SIGNS

[0052] 1—waste, 2—grate, 3—burner, 4—hearth, 5—initial waste particle, 6—ash, 10—upper boundary layer, 20—lower boundary layer, 30—bed combustion region.

DETAILED DESCRIPTION

[0053] The present invention will be further described below with reference to specific embodiments, however, the protection scope of the present invention is not limited thereto.

[0054] FIG. 1 is a schematic diagram of an incineration process of solid particles in a waste according to the present invention, the left side of FIG. 1 shows an incinerator, where a waste 1 is stacked on a grate 2 in a hearth 4, a burner 3 is arranged in the hearth 4, primary air is sent below the grate 2, a flue gas is discharged from an exhaust port above the hearth 4, the waste of a bed has a certain thickness, and the bed has an upper boundary and a lower boundary. The right side of FIG. 1 shows a process by which a waste is incinerated by initial waste particles 5 to an ash 6, the combustion of the waste in the bed is essentially a combustion of a porous medium formed by a solid waste stacked on the grate, the combustion process includes four sub-processes of moisture evaporation, volatile matter analysis, volatile matter combustion, and fixed carbon oxidation.

[0055] FIG. 2 is a schematic diagram of a modeling process for a combustion model of a bed of a waste incinerator according to the present invention. Referring to FIG. 2, according to the present invention, following measures are mainly adopted, to make up shortcomings of existing models in a targeted manner:

[0056] {circle around (1)} adding trace elements N and S to waste component elements;

[0057] {circle around (2)} increasing the chemical reaction between volatile matter and water vapor;

[0058] {circle around (3)} setting boundary conditions of a model as heat and mass transfer conditions to the exterior.

[0059] The technical schemes of the present invention are described in detail below. According to common technical terminology in the existing field, “municipal solid waste” is abbreviated as “waste” in some places below, and such abbreviation does not result in indefiniteness for those skilled in the art.

[0060] <Model of Combustion in a Bed of a Waste Incinerator>

[0061] A model of combustion in a bed of a waste incinerator according to the present invention includes a moisture evaporation model, a volatile matter analysis model, a volatile matter combustion model, and a fixed carbon combustion model, where by using the four models, a full process of waste incineration is formed.

[0062] <Moisture Evaporation Model>

[0063] After entering in an incinerator, a municipal solid waste is firstly heated by radiation in the incinerator and is subjected to heat exchange with a high-temperature gas, and the reaction rate equation is as follows:

R.sub.evp=A.sub.sh.sub.s(C.sub.w,s−C.sub.w,g)

[0064] where R.sub.evp is an evaporation rate of moisture, (kg/(m.sup.3.Math.s)), A.sub.s is an surface area of a calculation volume, in (m.sup.2), C.sub.w,s and C.sub.w,g are water vapor concentrations of a solid particle surface and a gas phase portion, respectively, and h.sub.s is a gas-solid two-phase mass transfer coefficient, in (m/s);

[00012]$C_{w,s}=\frac{P_{w,s}}{1000\mathrm{RT}}$$P_{w,s}=\exp \left(20.386-\frac{5132}{T}\right)\times 133.322$

[0065] where P.sub.w,s is a partial pressure of surface water of solid particles (Pa), R is an ideal gas constant (J/(mol.Math.K)), T is temperature (K). The gas-solid mass transfer coefficient h.sub.s may be calculated from the Thank number (Sh) and the Schmitt number (Sc) as follows:

h.sub.s=Sh×D.sub.g/d.sub.p

Sh=2+1.1Sc.sup.0.33Re.sup.0.6

Sc=μ/ρ.sub.gD.sub.g

[0066] where D.sub.g is a diffusion coefficient of a gas, in (m.sup.2/s), d.sub.p is a particle size of a solid particle (m), Re is the Reynolds number based on the particle size of the particle as the characteristic length, Re=ρ.sub.gUd.sub.p/μ, where μ is a dynamic viscosity coefficient of a gas, in (Pa.Math.s).

[0067] The calculation formula of the diffusion coefficient D.sub.g is as follows:

D.sub.g=D.sub.g.sup.e+0.5.Math.d.sub.p.Math.u

[0068] where D.sub.g.sup.e is a diffusion coefficient in the absence of fluid, which may be calculated using a binary diffusion coefficient as follows:

[00013]$D_{\mathrm{ij}}=\frac{0.00186T^{1.5}}{p{\sigma }_{\mathrm{ij}}^2\Omega }\sqrt{\frac{1}{M_i}+\frac{1}{M_j}}$

[0069] where i represents a computing component and j represents another component other than the component i.

[0070] <Volatile Matter Analysis Model>

[0071] Volatile matter in a waste component may be cracked into small molecular gases under a condition of heating, and a reaction rate equation is:

[00014]$R_v=A_v\exp \left(-\frac{E_v}{RT}\right){\rho }_s{Y}_v$

[0072] where R.sub.v is a rate in (kg/(m.sup.3.Math.s)), E.sub.v is the activation energy of a waste pyrolysis, E.sub.v=6.9×10.sup.7 (J/kmol), A.sub.v is a pre-factor of a waste pyrolysis rate, A.sub.v=3.4×10.sup.4; R is the ideal gas constant; T is reaction temperature in (K); ρ.sub.s is an apparent density of a solid waste, in (kg/m.sup.3); Y.sub.v is a mass ratio of volatile matter in a solid waste.

[0073] <Volatile Matter Combustion Model>

[0074] In the present model, volatile matters volatilized from a waste include CO, H.sub.2, CH.sub.4, NH.sub.3, and H.sub.2S. Combustion reaction equations and reaction rates of volatile matters of the present model are shown in Table 1. The reaction rate constants are all calculated according to the Arrhenius equation, as follows:

[00015]$k=A{T}^b\exp \left(-\frac{E}{\mathrm{RT}}\right)$

TABLE-US-00001 TABLE 1 Combustion Reaction Equations and Reaction Rates of Volatile matters with O.sub.2 chemical reaction reaction order H.sub.2 + 0.5O.sub.2 .fwdarw. H.sub.2O (g)  6.8 × 10.sup.15 −1  1.67 × 10.sup.8 [H.sub.2].sup.0.25[O.sub.2].sup.1.5 CH.sub.4 + 1.5O.sub.2 .fwdarw. CO + 2H.sub.2O (g) 5.012 × 10.sup.11   0    2 × 10.sup.8 [CH.sub.4].sup.0.7[O.sub.2].sup.0.8 CO + 0.5O.sub.2 .fwdarw. CO.sub.2 2.239 × 10.sup.12   0 1.702 × 10.sup.8 [CO][O.sub.2].sup.0.25[H.sub.2O].sup.0.5 NH.sub.3 + O.sub.2 .fwdarw. NO + 0.5H.sub.2 + H.sub.2O (g)  1.21 × 10.sup.5   2  6.65 × 10.sup.7 [NH.sub.3][O.sub.2].sup.0.5[H.sub.2].sup.0.5 H.sub.2S + 1.5O.sub.2 .fwdarw. SO.sub.2 + H.sub.2O (g)  6.5 × 10.sup.5   0  8.97 × 10.sup.7 [H.sub.2S][O.sub.2]

[0075] In addition to the combustion reaction equations of CO, H.sub.2, CH.sub.4, NH.sub.3, and H.sub.2S with O.sub.2 in Table 1, in the present model, reaction equations of volatile matters with water vapor are also included, specifically the reaction equations for CO and CH.sub.4 with water vapor, respectively, as shown in Table 2.

TABLE-US-00002 TABLE 2 Reaction Equations and Reaction Rates of Volatile matters with H.sub.2O chemical reaction A b E reaction order CH.sub.4 + H.sub.2O .fwdarw. CO + 3H.sub.2   3 × 10.sup.11 0 1.26 × 10.sup.8 [CH.sub.4][O.sub.2] CO + H.sub.2O .fwdarw. CO.sub.2 + H.sub.2 2.75 × 10.sup.12 0  8.4 × 10.sup.7 [CO][H.sub.2O]

[0076] Based on this, chemical reactions of selected gas phase components CO, H.sub.2, CH.sub.4, NH.sub.3, and H.sub.2S with O.sub.2, respectively, as well as chemical reactions of CO, CH.sub.4 with water vapor, respectively, construct a volatile matter combustion model of gas phase combustion of the waste according to the present invention.

[0077] <Fixed Carbon Combustion Model>

[0078] The coefficient of volatile matter represents the process of waste carbonization, and the fixed carbon may be ignited after the volatilization is completed. Since it is a combustion reaction, in which the oxidation reaction of the carbon is taken into account, the chemical equation is as follows:

C.sub.(s)+αO.sub.2.fwdarw.2(1−α)CO+(2α−1)CO.sub.2

[0079] where α is the coefficient of oxygen actually participating in the reaction, which is related to the generation ratios of CO and CO.sub.2, and which may be written as a function of current temperature T, as follows:

CO/CO.sub.2=250 exp(−6240/T)

the reaction rate is:

R.sub.c=P.sub.O.sub.2/(1/k.sub.r+1/k.sub.d)

[0080] where α is a consumption coefficient of oxygen, R.sub.c is a consumption rate of the fixed carbon, in (kg/(m.sup.3.Math.s)), P.sub.O.sub.2 is the partial pressure of oxygen, k.sub.r, k.sub.d are chemical reaction rate coefficients and oxygen diffusion coefficients, respectively, the chemical reaction parameter k.sub.r dominates the reaction rate,

[00016]$k_r=A_c\exp \left(-\frac{E_c}{\mathrm{RT}}\right),\mathrm{where}$$A_c=3\mathrm{kg}/\left(m^{2}s\mathrm{kPa}\right),E_c/R=10300.$

[0081] <Governing Equations>

[0082] The governing equations according to the present invention are N-S (Navier-Stokes equations) equations established for a solid phase and a gas phase, respectively, based on three laws of conservation of mass, conservation of momentum, and conservation of energy, and describe combustion phenomena such as flow, diffusion, and reaction of the solid phase and the gas phase in a calculation area in a bed of a waste. The governing equations include a continuity equation, a momentum equation, an energy equation, and a component equation, which are specifically described as follows.

[0083] <Continuity Equation>

[0084] The continuity equation is the mass conservation equation, and the equation of a gas phase part is:

[00017]$\frac{\partial \left(\varphi {\rho }_g\right)}{\partial t}+\mathrm{div}\left(\varphi {\rho }_{g}u\right)=S_g$

[0085] the equation for a solid phase part is:

[00018]$\frac{\partial {\rho }_s}{\partial t}=-S_g$

[0086] where ϕ is a void fraction (%), ρ.sub.g is a density of a gas, in (kg/m.sup.3), u is a flow rate of a gas (m/s), ρ.sub.s is a density of a solid, in (kg/m.sup.3), S.sub.g is a source phase of the gas phase continuity equation, the value of which is the sum of reaction rates of solid phase to gas phase reactions (including moisture evaporation, volatile matter precipitation, and fixed carbon oxidation).

[0087] <Momentum Equation>

[0088] The flow of fluid in a porous medium is primarily affected by pressure, adhesive force, gas-solid surface traction force, and self-gravity. Due to that the fluid is a gas, the influence of the self-gravity is neglected, and the adhesive force and the gas-solid surface traction force are calculated by adopting an Ergun formula, to obtain a momentum governing equation as follows:

[00019]$\frac{\partial \left(\varphi {\rho }_{g}u\right)}{\partial t}+\mathrm{div}\left(\varphi {\rho }_g\mathrm{uu}\right)=-\nabla P-\frac{\mu u}{K}-{\mathrm{\beta \rho }}_g{u}^2$

[0089] where P is the pressure of a gas, in (Pa), K is the permeability of a porous medium, β is a traction coefficient, and the calculation formulae are as follows:

[00020]$\frac{1}{K}=150\frac{{\left(1-\varphi \right)}^2}{{\varphi }^3{d}_p^2}$$\beta =\frac{1.75\left(1-\varphi \right)}{d_p{\varphi }^3}$

[0090] <Energy Equation>

[0091] The energy equation is the thermal equilibrium equation of a system, including three parts for material heat conduction, convection heat dissipation and reaction endotherm and exotherm. In the present invention, assuming that the temperature in a same computing unit is uniform and the temperature of both a gas phase and a solid phase are the same, the energy equation is as follows:

[00021]$\frac{\partial \left(\varphi {\rho }_g{C}_{{}_{\mathrm{pg}}}T+\left(1-\varphi \right){\rho }_s{C}_{ps}T\right)}{\partial t}+\mathrm{div}\left({\mathrm{\varphi \rho }}_g{\mathrm{uC}}_{\mathrm{pg}}T\right)=\mathrm{div}\left(k_{\mathrm{eff}}\nabla T\right)+S_T$

[0092] where C.sub.ps is a specific heat capacity of a solid, in (J/kg), C.sub.pg is a specific heat capacity of a gas, in (J/kg), k.sub.eff is an effective thermal conductivity of a bed, in (W/(m s)), and S.sub.T is the source phase of the energy equation.

[0093] In the effective thermal conductivity k.sub.eff, the thermal conductivity of a gas and a solid is comprehensively taken into account, as well as the radiant heat between solid particles, and the calculation formula is:

[00022]$k_{\mathrm{eff}}=k_{\mathrm{eff},0}+0.5{\mathrm{PrRek}}_g$$k_{\mathrm{eff},0}=\varphi \left(k_g+h_{\mathrm{rv}}\Delta l\right)+\frac{\left(1-\varphi \right)\Delta l}{1/\left(k_g/l_v+h_{\mathrm{rs}}\right)+l_s/k_s}$

[0094] where k.sub.eff,0 is an effective thermal conductivity in the absence of fluid, in (W/(m.Math.s)), Re is the Reynolds number with a particle size of a solid particle as the characteristic length; h.sub.rv is an effective radiant heat transfer coefficient in void (W/(m.sup.2.Math.K)), h.sub.rs is an effective radiant heat transfer coefficient of a solid contact surface (W/(m.sup.2.Math.K)), Δl is a characteristic length between two solid particles (mm), l.sub.s is the equivalent thickness of a fluid calculation layer, in (mm), k.sub.s is a thermal conductivity of a solid, in (W/(m.Math.K)), and l.sub.v is the thickness of a gas-solid contact layer, in (mm).

[0095] <Component Equation>

[0096] The component equation is essentially a single-component continuity equation in a gas or a solid, the component equation of a gas phase part is:

[00023]$\frac{\partial \left(\varphi {\rho }_g{Y}_{\mathrm{ig}}\right)}{\partial t}+\mathrm{div}\left(\varphi {\rho }_g{Y}_{\mathrm{ig}}\right)=\mathrm{div}\left(D_{\mathrm{ig}}\nabla Y_{\mathrm{ig}}\right)+S_{Y_{\mathrm{ig}}}$

[0097] where Y.sub.ig is a mass fraction of an i-th gas component in a mixed gas, gas components in the mixed gas includes N.sub.2, O.sub.2, CH.sub.4, CO, CO.sub.2, H.sub.2, NH.sub.3, H.sub.2S, SO.sub.2, NO, and H.sub.2O; D.sub.ig is a diffusion coefficient of a corresponding gas component, in (m.sup.2/s), and S.sub.Y.sub.ig is a source phase of a corresponding component; [0098] the component equation of a solid phase part is:

[00024]$\frac{\partial {\rho }_{\mathrm{is}}}{\partial t}=r_{\mathrm{is}}$

[0099] where ρ.sub.is is a density of an i-th component in a solid particle, in (kg/m.sup.3), i represents moisture, volatile matter, fixed carbon and ash in a solid particle, and r.sub.is is a reaction rate of a corresponding component, in (kg/(m.sup.3.Math.s)).

[0100] <Boundary Condition>

[0101] FIG. 3 shows a bed combustion area of a model according to the present invention, the direction of arrows points to the outlet of a flue gas, a waste is in contact with the exterior at an upper boundary layer 10 and a lower boundary layer 20 of the bed combustion, the bed combustion area 30 transfers heat and mass with a hearth at the upper boundary layer 10, the bed combustion area 30 transfers heat and mass with the bottom at the lower boundary layer 20, therefore boundary conditions are the heat and mass transfer equations of the upper and lower boundary layers to the exterior.

[0102] <Upper Boundary Condition>

[0103] The upper boundary of the waste incineration bed is in contact with the waste hearth, the pressure boundary is set to atmospheric pressure, the velocity boundary is set to be gradient zero, and the mass transfer boundary find expression in the boundary condition equation of the component equation as follows:

[00025]$D_{g}A\frac{\partial Y_g}{\partial x}{.Math.}_s=A{h}_s\left(Y_{\infty }-Y_{g,s}\right)$

[0104] where A is an area of a bed interface, in (m.sup.2), D.sub.g is a diffusion coefficient of a gas, in (m.sup.2/s), h.sub.s is a mass transfer coefficient, in (m/s), Y.sub.∞ is a mass fraction of a component gas in a hearth, and Y.sub.g,s is a mass fraction of a component gas in an upper boundary layer.

[0105] The heat transfer boundary is as follows:

[00026]$k_{\mathrm{eff}}A\frac{\partial T}{\partial x}{.Math.}_s=A{h}_T\left(T_{\infty }-T_{s1}\right)+A\mathrm{.Math.\sigma }\left(T_{r\mathrm{ad}}^4-T_{s1}^4\right)$

[0106] where k.sub.eff is an effective thermal conductivity coefficient of a bed, in (W/(m.Math.s)), h.sub.T is a heat transfer coefficient in (W/(m.sup.2.Math.K)), T.sub.∞ is temperature in a hearth, in (K), T.sub.rad is radiation temperature in (K), T.sub.s1 is temperature of an upper boundary layer, in (K), ε is a radiation coefficient, ε is 0.8, σ is the Boltzmann's constant.

[0107] The heat transfer coefficient h.sub.T may be calculated by the Planck constant (Pr) and the Knoop number (Nu), as follows:

[00027]$h_T=\mathrm{Nu}\times k_g/d_p$$\mathrm{Nu}=2+1.1{\mathrm{Pr}}^{0.33}{\mathrm{Re}}^{0.6}$$\mathrm{Pr}=\frac{\mu C_{\mathrm{pg}}}{k_g}$

[0108] where k.sub.g is a thermal conductivity coefficient of a gas, in (W/(m.Math.K)), C.sub.pg is a specific heat capacity of a gas, in (J/(kg.Math.K)), d.sub.p is a particle size of a solid particle, in (m).

[0109] <Lower Boundary Condition>

[0110] The lower boundary of a waste incineration bed is in contact with the exterior, the pressure boundary is set to atmospheric pressure, the velocity boundary is set to a constant, and the mass transfer boundary find expression in the boundary condition equation of the component equation as follows:

[00028]${D_{g}A\frac{\partial Y_g}{\partial x}.Math.}_s={\mathrm{Ah}}_s\left(Y_{\mathrm{in}}-Y_{g.s}\right)$

[0111] where D.sub.g is a diffusion coefficient of a gas, in (m.sup.2/s), h.sub.s is a mass transfer coefficient in (m/s), Y.sub.in is a mass fraction of a component gas in the exterior, and Y.sub.g,s is a mass fraction of a component gas in a lower boundary layer;

[0112] the heat transfer boundary is as follows:

[00029]${k_{\mathrm{eff}}A\frac{\partial T}{\partial x}.Math.}_s={\mathrm{Ah}}_T\left(T_{\mathrm{in}}-T_{s2}\right)+A\mathrm{.Math.\sigma }\left(T_{\mathrm{in}}^4-T_{s2}^4\right)$

[0113] where k.sub.eff is an effective thermal conductivity of a bed, in (W/(m.Math.s)), h.sub.T is a heat transfer coefficient in (W/(m.sup.2.Math.K)), T.sub.in is temperature of exterior (K), and T.sub.s2 is temperature of a lower boundary layer (K).

[0114] <Model Solution>

[0115] In the present application, all governing equations include four terms of a transient term, a convection term, a diffusion phase, and a source phase (the convection term and the diffusion phase do not exist in a portion of equations, which may be seen as a correlation coefficient of zero), and all governing equations may be written into a generic format equation, as follows:

[00030]$\frac{\partial \left(\mathrm{\rho \Phi }\right)}{\partial t}+\mathrm{div}\left(\rho u\Phi \right)=\mathrm{div}\left(\lambda \nabla \Phi \right)+S_{\Phi }$

[0116] where ρ is a density, u is a velocity, λ is a diffusion coefficient, Φ is a solved variable, and S.sub.Φ is a corresponding source phase. The discretization of the governing equation may adopt a finite volume method, a bed calculation area is divided into a limited number of calculation volumes, all the governing equations are discretized into each finite volume, during the discretization process, a central differential format is used for the convection term, and a full implicit mode is adopted for the diffusion phase, linear processing is adopted for the source phase, so that each control equation may be discretized into the form of a linear matrix, and a SIMPLE algorithm is adopted for programming and solving. The finite volume method and the SIMPLE algorithm are algorithms known in computational fluid mechanics, and the principles and processes thereof are not repeated here. The computational process according to the present invention may be calculated and solved by writing Code BASIC (Bulk Accumulated Solids Incineration Code) by means of a MATLAB programming platform.

[0117] By applying the model of the present invention, a combustion process of a bed of a waste incinerator is calculated, input for calculation includes element analysis data, industrial analysis data, Lower Heating Value (LHV) and size data of a waste raw material, in addition, input for calculation also includes a primary air volume, initial exterior temperature, the amount of a waste fed into a furnace, the equivalent spherical diameter of a waste size, a stacking bed height, an apparent density, a void fraction, a high-temperature radiant heat source at the top of a hearth and a radiation rate of a waste bed. Further, output for calculation includes distributions of a temperature field, a concentration field of each substance, a pressure field, and a flow field during incineration of a waste in a bed. Since elements N and S in a waste component are taken into account in the method of the present invention, output results include concentration fields of NOx, and SOx contaminants.

[0118] Note that, for a same calculation model, different programming platforms and different program statements may be used for programming calculation. The present invention does not limited to a specific programming calculation scheme. As long as it is a method that may solve and calculate the model and obtain the calculation results, the method may be used.

Embodiment 1

[0119] In the present invention, experimental verification is carried out on a model of combustion in a bed of a waste incinerator according to the present invention in a form of comparison of experimental data with simulation calculation data of the model according to the present invention. Initial parameters for the model of combustion in a bed of a waste incinerator according to the present invention are set to be consistent with experimental data, and the mass of a solid and the concentrations of various gas components in simulation results are compared with experimental measured values.

[0120] The experimental data is the experiment data of waste incineration of a fixed bed incinerator. The incineration of a waste in a furnace has the characteristics of stacked materials and conforms to the simulation conditions of the model according to the present invention; further, it is relatively easy to control a fixed bed equipment, and it is easy to perform a detection under laboratory conditions. The details are described below.

[0121] (1) Experimental Apparatus

[0122] The fixed bed has an inner diameter of 0.2 m and a total height of 1.5 m, and has a plurality of ventilation holes at a bottom of a grate with the diameter of 2 mm and accounting for 7% of the whole grate area; primary air passes through an air pump, a flowmeter and a preheating system, which enters from a bottom grate and provides oxygen for incineration of a solid waste; secondary air is introduced from the top and provides oxygen for ignition of a combustor, and the combustor is arranged at 750 mm above the grate; solid waste is stacked in an lower area in the fixed bed (as a simulation calculation area), and a thermocouple is arranged in the area to detect temperature change of the experiment; a gas collection device is arranged at the height of 430 mm from the height of the grate, the component analysis of a flue gas is carried out through a flue gas analyzer and a data collection system, and the gas components, such as O.sub.2, CO.sub.2, CO and the like may be analyzed and detected, finally, the results of detection and analysis may be used to be compared with simulation computation data of the model according to the present invention.

[0123] (2) Analysis of Raw Materials

[0124] The experimental materials used in the experiment are raw wastes with an average calculation size of 12 mm, and industrial analysis and element analysis of the raw materials are shown in Table 3:

TABLE-US-00003 TABLE 3 Element Analysis and Industrial Analysis of Raw Wastes industrial analysis (%) elemental analysis (%) volatile fixed LHV C H O N S moisture matter carbon ash (kJ/kg) 28.6 3.3 29.8 0 0 35.0 53.3 8.4 3.3 9000

[0125] According to data in Table 3 and the calculation method of volatile matters in the present invention, the volatile matters and the component gases thereof may be calculated as follows:

CH.sub.1.960396O.sub.1.1054356≡0.343035844CO+0.3816999CO.sub.2+0.429669507H.sub.2+0.275264256CH.sub.4

[0126] (3) Initial Conditions

[0127] The initial conditions set in the model according to the present invention are consistent with experimental conditions, the initial conditions are set as follows: primary air volume u=2001/min, initial exterior temperature T.sub.in=15° C., amount of waste fed into furnace 2.02 kg, equivalent spherical diameter of waste size D=12 mm, stacking bed height H=480 mm, apparent density ρ.sub.s=137 kg/m.sup.3, void fraction set to ϕ=0.65, high temperature radiant heat source at the top of hearth set to T.sub.rad=1173 K, and radiation rate of waste bed set to ε=0.8.

[0128] (4) Verification Results

[0129] 1) Solid Mass

[0130] FIG. 4 is a graph of percentages of residual mass of solid wastes in a bed, where the horizontal axis shows reaction time, the vertical axis shows percentages of residual mass of a solid (%), the curve shows simulation data, and the points show experimental data. As may be seen from FIG. 4, simulation results are well matched with experimental data and their trends are consistent.

[0131] 2) Temperature Distribution

[0132] FIG. 5 is a curve graph of temperature at different height positions of a bed, the height is selected at 430 mm, 340 mm, 250 mm, and 160 mm above a grate, respectively. In FIG. 5, the horizontal axis shows combustion time, the vertical axis shows temperature. Temperature rise time at different positions of the bed is different, since a high-temperature radiation comes from the hearth at the top of the bed, the waste solid at the top initially heats up. As may be seen from FIG. 5, the 430 mm height begins to warm at 200 s, the 340 mm height begins to warm at 420 s, the 250 mm height begins to warm at 680 s, the 160 mm height begins to warm at 900 s, at the last, after 1450 s, all of them are cooled to the temperature of the primary air.

[0133] FIG. 6 is a curve graph of temperature variations and velocity variations at the top of a calculation area. As may be seen, the trend of the velocity curve is consistent with that of the temperature curve. When the top layer burns stably, the temperature is about 1300 K, the flow rate of the gas fed into furnace is 0.1065 m/s, and the steady-state flow rate is about 0.8 m/s.

[0134] 3) Oxygen Concentration

[0135] FIG. 7 is a comparison of calculation results versus experimental results for oxygen concentration at 430 mm, in which the curve shows simulation results, and the points show experimental results. From the curve, it may be seen that the predicted value is very close to the experimental value, while the four stages of non-ignition, ignition, stable combustion and burnout of waste are shown; before ignition, the mole fraction of oxygen is 21% of the air concentration and is rapidly reduced after ignition; when the stable combustion state is achieved, the oxygen supply and the oxygen consumption are equal, the mole fraction of oxygen is maintained dynamic equilibrium at 0, the oxygen is no longer consumed after the fixed carbon and the gas phase combustible component are burned out, and the oxygen is rapidly recovered to the air concentration level.

[0136] 4) CO.sub.2 Concentration

[0137] FIG. 8 is a comparison of calculation results versus experimental results for carbon monoxide concentration at 430 mm, in which the curve shows simulation results, and the points show experimental results. In FIG. 8, the change in CO.sub.2 concentration is the same as that of oxygen, and both experience four stages of the non-ignition stage, the ignition stage, the stable combustion stage and the burnout stage, the simulation data and the experimental data are well matched at each stage, and the simulation data is approximately 3% lower than the experimental data at the stable combustion stage.

[0138] 5) CO Concentration

[0139] FIG. 9 is a comparison of calculation results versus experimental results for carbon monoxide concentration at 430 mm, in which the curve shows simulation results, and the points show experimental results. From FIG. 9, it may be seen that the simulation results have good correlation with experimental data.

[0140] The above verification results show that, in the case that simulation conditions are consistent with experimental conditions, the variation trend of a simulation curve for a solid mass, an oxygen concentration, a CO.sub.2 concentration, and a CO concentration and the like in a bed is consistent with that of actual measurement data, and calculated values are very close to actual values, which proves that accurate calculation results are obtained by applying the method of the present invention.

[0141] The present invention is not limited to embodiments described above, and without departing from the essential contents of the present invention, any variations, improvements, and/or substitutions that may be conceived by those skilled in the art fall within the scope of the present invention.